18,123 research outputs found
Path-tracing Monte Carlo Library for 3D Radiative Transfer in Highly Resolved Cloudy Atmospheres
Interactions between clouds and radiation are at the root of many
difficulties in numerically predicting future weather and climate and in
retrieving the state of the atmosphere from remote sensing observations. The
large range of issues related to these interactions, and in particular to
three-dimensional interactions, motivated the development of accurate radiative
tools able to compute all types of radiative metrics, from monochromatic, local
and directional observables, to integrated energetic quantities. In the
continuity of this community effort, we propose here an open-source library for
general use in Monte Carlo algorithms. This library is devoted to the
acceleration of path-tracing in complex data, typically high-resolution
large-domain grounds and clouds. The main algorithmic advances embedded in the
library are those related to the construction and traversal of hierarchical
grids accelerating the tracing of paths through heterogeneous fields in
null-collision (maximum cross-section) algorithms. We show that with these
hierarchical grids, the computing time is only weakly sensitivive to the
refinement of the volumetric data. The library is tested with a rendering
algorithm that produces synthetic images of cloud radiances. Two other examples
are given as illustrations, that are respectively used to analyse the
transmission of solar radiation under a cloud together with its sensitivity to
an optical parameter, and to assess a parametrization of 3D radiative effects
of clouds.Comment: Submitted to JAMES, revised and submitted again (this is v2
The development of local solar irradiance for outdoor computer graphics rendering
Atmospheric effects are approximated by solving the light transfer equation, LTE, of a given viewing path. The resulting accumulated spectral energy (its visible band) arriving at the observer’s eyes, defines the colour of the object currently on the line of sight. Due to the convenience of using a single rendering equation to solve the LTE for daylight sky and distant objects (aerial perspective), recent methods had opt for a similar kind of approach. Alas, the burden that the real-time calculation brings to the foil had forced these methods to make simplifications that were not in line with the actual world observation. Consequently, the results of these methods are laden with visual-errors. The two most common simplifications made were: i) assuming the atmosphere as a full-scattering medium only and ii) assuming a single density atmosphere profile. This research explored the possibility of replacing the real-time calculation involved in solving the LTE with an analytical-based approach. Hence, the two simplifications made by the previous real-time methods can be avoided. The model was implemented on top of a flight simulator prototype system since the requirements of such system match the objectives of this study. Results were verified against the actual images of the daylight skies. Comparison was also made with the previous methods’ results to showcase the proposed model strengths and advantages over its peers
The Fate of the First Galaxies. I. Self-Consistent Cosmological Simulations with Radiative Transfer
In cold dark matter (CDM) cosmogonies, low-mass objects play an important
role in the evolution of the universe. Not only are they the first luminous
objects to shed light in a previously dark universe, but, if their formation is
not inhibited by their own feedback, they dominate the galaxy mass function
until redshift z \sim 5. In this paper we present and discuss the
implementation of a 3D cosmological code that includes most of the needed
physics to simulate the formation and evolution of the first galaxies with a
self-consistent treatment of radiative feedback. The simulation includes
continuum radiative transfer using the ``Optically Thin Variable Eddington
Tensor'' (OTVET) approximation and line-radiative transfer in the H_2
Lyman-Werner bands of the background radiation. We include detailed chemistry
for H_2 formation/destruction, molecular and atomic cooling/heating processes,
ionization by secondary electrons, and heating by Ly\alpha resonant scattering.
We find that the first galaxies ("small-halos") are characterized by a
bursting star formation, self-regulated by a feedback process that acts on
cosmological scales. Their formation is not suppressed by feedback processes;
therefore, their impact on cosmic evolution cannot be neglected. The main focus
of this paper is on the methodology of the simulations, and we only briefly
introduce some of the results. An extensive discussion of the results and the
nature of the feedback mechanism are the focus of a companion paper.Comment: Accepted for publication on ApJ, 33 pages, including 14 figures and 2
tables. Movies and a higher quality version of the paper (figures) are
available at: http://casa.colorado.edu/~ricotti/MOVIES.htm
Rzsweep: A New Volume-Rendering Technique for Uniform Rectilinear Datasets
A great challenge in the volume-rendering field is to achieve high-quality images in an acceptable amount of time. In the area of volume rendering, there is always a trade-off between speed and quality. Applications where only high-quality images are acceptable often use the ray-casting algorithm, but this method is computationally expensive and typically achieves low frame rates. The work presented here is RZSweep, a new volume-rendering algorithm for uniform rectilinear datasets, that gives high-quality images in a reasonable amount of time. In this algorithm a plane sweeps the vertices of the implicit grid of regular datasets in depth order, projecting all the implicit faces incident on each vertex. This algorithm uses the inherent properties of a rectilinear datasets. RZSweep is an object-order, back-toront, direct volume rendering, face projection algorithm for rectilinear datasets using the cell approach. It is a single processor serial algorithm. The simplicity of the algorithm allows the use of the graphics pipeline for hardware-assisted projection, and also, with minimum modification, a version of the algorithm that is graphics-hardware independent. Lighting, color and various opacity transfer functions are implemented for giving realism to the final resulting images. Finally, an image comparison is done between RZSweep and a 3D texture-based method for volume rendering using standard image metrics like Euclidian and geometric differences
Shape: A 3D Modeling Tool for Astrophysics
We present a flexible interactive 3D morpho-kinematical modeling application
for astrophysics. Compared to other systems, our application reduces the
restrictions on the physical assumptions, data type and amount that is required
for a reconstruction of an object's morphology. It is one of the first publicly
available tools to apply interactive graphics to astrophysical modeling. The
tool allows astrophysicists to provide a-priori knowledge about the object by
interactively defining 3D structural elements. By direct comparison of model
prediction with observational data, model parameters can then be automatically
optimized to fit the observation. The tool has already been successfully used
in a number of astrophysical research projects.Comment: 13 pages, 11 figures, accepted for publication in the "IEEE
Transactions on Visualization and Computer Graphics
FluoRender: An application of 2D image space methods for 3D and 4D confocal microscopy data visualization in neurobiology research
Journal Article2D image space methods are processing methods applied after the volumetric data are projected and rendered into the 2D image space, such as 2D filtering, tone mapping and compositing. In the application domain of volume visualization, most 2D image space methods can be carried out more efficiently than their 3D counterparts. Most importantly, 2D image space methods can be used to enhance volume visualization quality when applied together with volume rendering methods. In this paper, we present and discuss the applications of a series of 2D image space methods as enhancements to confocal microscopy visualizations, including 2D tone mapping, 2D compositing, and 2D color mapping. These methods are easily integrated with our existing confocal visualization tool, FluoRender, and the outcome is a full-featured visualization system that meets neurobiologists' demands for qualitative analysis of confocal microscopy data
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